free-ebook-crude-oil-desalting.pdf

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To obtain a copy of the full ebook and all the chapters listed in the table of contents

please visit www.crudeoildesalting.com

Devlin Jones, [email protected]

CRUDE OIL DESALTING

A comprehensive guide to understanding and operating a modern crude oil desalter

www.crudeoildesalting.com

Table of Contents

1. Introduction..................................................................................................................... 1

2. About the Author ............................................................................................................ 6

3. General Desalting Process Overview.............................................................................. 8

Salt Removal................................................................................................................. 10

Sediment and BS&W Removal .................................................................................... 11

Metals and other Contaminant Removal....................................................................... 13

4. Desalter Controls ..........................................................................................................N/A

Wash Water...................................................................................................................N/A

Injection Locations....................................................................................................N/A

Wash Water Sources .................................................................................................N/A

Mix Valve .....................................................................................................................N/A

Rag or Interface Control and Remediation ...................................................................N/A

Solids Management, BS&W and Mud busting.............................................................N/A

Solids Removal Strategy...........................................................................................N/A

Chemicals..................................................................................................................N/A

Electrostatic Grid ..........................................................................................................N/A

Volts..........................................................................................................................N/A

Amperage..................................................................................................................N/A

Temperature Control.....................................................................................................N/A

Level Control ................................................................................................................N/A

Online Level Control ................................................................................................N/A

Manual Samples........................................................................................................N/A

Pressure Control............................................................................................................N/A

5. Desalter Chemicals .......................................................................................................N/A

Basic Chemicals............................................................................................................N/A

Injection Location .....................................................................................................N/A

Demulsifier Selection................................................................................................N/A

Disclaimer of liability: www.crudeoildesalting.com and its authors produced this product as a general guide to crude oil desalting for informational purposes only. All

recommendations contained in this document are advisory only with no guarantees or representations of results. Before any information in this document is used or implemented it

should be thoroughly reviewed by a subject matter expert. www.crudeoildesalting.com and its authors shall not be liable for any indirect, punitive, exemplary of consequential

damages or losses from any cause whatsoever including but not limited to negligence.

i

Advanced Chemicals ....................................................................................................N/A

Caustic Injection .......................................................................................................N/A

Solids Conditioning Chemicals.................................................................................N/A

Mud Wash Water Polymer........................................................................................N/A

Wash Water Polymer ................................................................................................N/A

Metal Passivators ......................................................................................................N/A

Chemical Systems.....................................................................................................N/A

6. Lab Testing ...................................................................................................................N/A

Common Desalter Tests................................................................................................N/A

Salt content as NaCl..................................................................................................N/A

BS&W and Solds ......................................................................................................N/A

Common Metals........................................................................................................N/A

pH..............................................................................................................................N/A

Other Tests ................................................................................................................N/A

7. Crude Slate Management..............................................................................................N/A

Crude Blend Compatibility ...........................................................................................N/A

Salt and Sediment Content............................................................................................N/A

API Gravity...................................................................................................................N/A

8. Post Desalter Treatment................................................................................................N/A

Desalted Crude..............................................................................................................N/A

Brine..............................................................................................................................N/A

9. Performance Monitoring and Optimization ..................................................................N/A

Key Performance Indicators .........................................................................................N/A

Selected Calculations ........................................................................................................N/A

Desalting Efficiency......................................................................................................N/A

Dehydration Efficiency.................................................................................................N/A

Solids Removal Efficiency ...........................................................................................N/A

Selected Conversions ....................................................................................................N/A

Calculating parts per million (PPM).........................................................................N/A

Conversion from ppm to PTB...................................................................................N/A Disclaimer of liability: www.crudeoildesalting.com and its authors produced this product as a general guide to crude oil desalting for informational purposes only. All




ii

10. Chemical Vendor Selection ........................................................................................N/A

The Right Desalter Chemical........................................................................................N/A

Corporate Technical Support ........................................................................................N/A

Local Support................................................................................................................N/A

Cost $$$ ........................................................................................................................N/A

11. Realistic expectations..................................................................................................N/A





iii

1. Introduction

According to the US Energy Administration Association the United States has a refining

capacity of over 18 million barrels per day. If most of the refineries are currently in

operation we can assume that just in the US alone there is close to 15 to 17 million

barrels of crude oil flowing though refineries every single day. On a world scale that

number can easily be doubled when taking into account the existence of super refineries

such as the Reliance Refinery in India that has over 1 million barrels per day of capacity.

When we think of refineries it is typically in the form of refining margins by making

gasoline (petrol) and diesel as the primary components. An incredible amount of training

is typically provided to operations and engineering on how to profitably run these

refineries in a reliable manner. Due to the complexity of making a barrel of gasoline or

diesel it is necessary to train individuals in separation, cracking, and reaction

technologies which can become a lifelong study with new technology in catalysts and

instrumentation being continually developed. Due to the complexity and vastness of

knowledge required to viably operate a modern refinery it is necessary for individuals to

eventually specialize in a refining field such as hydrotreating or distillation.

A typical refinery setup will be divided up into business units or areas where integrated

clusters of unit operations are managed by a specific team. This team will consist of

operations, engineering, integrity, reliability and maintenance. You can for example have

a crude unit area which will consist of the crude train all the way from the desalter inlet to

the vacuum distillation unit outlet. In such a business unit the engineers and operators

will focus on the overall throughput while meeting all their KPIs (key performance

indicators). Training will be provided in all of the core processes such as distillation

while smaller seemingly insignificant units such as the desalter will be treated as an

afterthought.





1

Technologies such as desalting and other non-core processes will typically take a back

seat to other core technologies such as LP modeling, distillation and hydrotreating. Not

only is there no direct cost benefit to optimizing a desalter but it is also not typically seen

as a very glamorous specialization. Most engineers and operators tend to ignore the

desalter until it becomes problematic and starts holding up production. Most of the major

and super major oil companies will have individuals on their staff with the needed

knowledge and experience to operate desalters but smaller and midsize companies will

often rely 100% on outside assistance. Even in large oil companies the desalter specialists

will typically be tasked with global responsibilities with little time to focus on one

individual desalter for too long unless it is proving to be very problematic. For this

reason, even though virtually all refineries in the world use a crude oil desalter the topic

is often misunderstood and most desalters operate well below their capability.

Without adequate desalting, even the most efficient refinery with the latest technology

can periodically face production cuts from a desalter acting as a bottleneck. Even if a

refinery never experiences the desalter as a bottleneck it can eventually have numerous

reliability problems associated with lack adequate desalting such as corroded crude tower

overheads, fouled furnaces, catalyst degradation, fouled distillation trays and general unit

corrosion. It is not uncommon for a refiner to reply that their desalter is operating just

fine only to complain later on that they are seeing accelerated corrosion rates compared

with expected design. They may then spend an inordinate amount of money on corrosion

inhibitors and metallurgy upgrades not realizing that the desalter is the root cause.

Due to the changes in crude oil sources that took place in the last 10-20 years, more and

more refineries process difficult crude such as Venezuelan and Canadian Oil Sands

crude. These new crude sources often poses a higher risk of causing problems in a

refinery due to high salt, metals and BS%W content. Even conventional crude sources are

changing as new techniques to improve well production are implemented. It is not

uncommon for a refinery to process the same crude source for 20 years only to be faced

with increasingly complex crude slates due to numerous well production chemicals Disclaimer of liability: www.crudeoildesalting.com and its authors produced this product as a general guide to crude oil desalting for informational purposes only. All




2

present. The changes in crude not only require diligence from the refiners to ensure that

distillation cuts are still adequate but also to ensure that it can still be effectively desalted.

Alarmingly it is often found that oil companies put almost all their trust in a chemical

vendor to provide expert knowledge on the operation of the desalter. The idea is that

these large chemical companies, selling specialized demulsifier chemistries, have

accumulated vast amounts of knowledge over the years which can be used to optimize

desalting units. Oil companies consequently spend very little R &D (research and

development) and training dollars on desalting and become slaves to their chemical

vendors. This trust then leads to a false level of comfort and that is seldom warranted

It is true that most chemical vendors have multiple desalting experts on their payroll. The

major vendors will usually employ one or two true experts and then have a large group

claiming to be experts based on taking a one week desalter course or having looked after

a sales account where there happened to be a desalter. The true experts are typically

engineers or scientists with prior experience working for an oil company which enables

them to understand the chemistry as well as the overall impact of desalter operation.

The big problem in relying on the chemical vendor to be the desalter expert lies in the

fact that the majority of site support personnel working for the chemical companies are

completely clueless. Their knowledge, if theyve been with the company for a couple of

years, is usually based on a 3-5 day training course where they learn recipes of when this

happens do this. In some cases vendors will place a site representative straight out of

university or technical college and expect them to advise a world class refinery on how to

operate. These individuals are usually hired for their sales prowess and not their technical

acumen so the fact that they have zero practical experience does not bother the chemical

vendor. The site support salesman will then rely on the limited number of true experts in

their company to support them when difficult situation arise. You may then up with 2 true

desalting experts supporting 20 field salesmen.





3

On occasion a refinery will be lucky enough to have an experienced engineer employed

by the chemical vendor to look after their refinery. These individuals can be invaluable

since they are dedicated to keeping one piece of the unit running optimally while freeing

up time for the oil company engineers to look after the rest. This is however the

exception and not the rule.

From my unit operations experience I learned that it is impossible to understand a unit

purely through reading a book or taking a course. Quite often the best engineers I have

encountered take minimal formal training and instead spend hours upon hours learning

their units and obtaining mentorship from more experienced engineers. The only way to

truly understand the desalting unit is therefore to combine book knowledge with practical

operating experience. It is unfortunately not always possible to fast track practical

experience as virtually any unit operator will tell you. Every single time I was at a facility

during a crisis mode we immediately consulted the old timers at the site who have been

around for 20-30 years to find out what they did the last time something similar

happened. In some cases they provided an immediate solution and other cases we were

able to use the information they provided to come up with a viable solution.

If a book cant teach you everything you need to know about a desalter you may ask why

you should read this specific one. It is true that neither this book nor any other book or

course will give you what you need to go into a refinery and start operating a desalter.

The objective of this book is to provide book knowledge to those individuals with

existing operating experience thereby enabling them to optimize and troubleshoot a

desalter with little or no third party assistance. Most operators already have all the tools

required to solve virtually any desalter problem but they need some guidance and

background knowledge to put it in action.

If you are a new operator or engineer in a refinery just getting started this book will be a

valuable reference to help you understand what you see in the operating unit. You can

read about different topics and then discuss this with the experienced operators and Disclaimer of liability: www.crudeoildesalting.com and its authors produced this product as a general guide to crude oil desalting for informational purposes only. All




4

engineers enabling you to stay on a steep learning curve. It is important to recognize that

you will gain the necessary book knowledge to understand a desalter but will still need

assistance from experienced unit operators on how to apply that knowledge.

We are entering an era were many baby boomers will be retiring from their jobs at

refineries and it is critical that we get the young new operators and engineers up to speed

as quick as possible. Relying on third party chemical vendors to train new employees

should be used as a last resort since they are going through the same baby boomer cycle

and is just as short in experienced employees as most oil companies.





5

2. About the Author

I am currently employed as a professional chemical engineer and have spent my entire

career in the oil industry in fields ranging from conventional oil refining to dealing with

the heaviest of oil sands feeds.

I started my career in the engineering design and construction fields where I saw first

hand how decisions are made for new facilities and how difficult it is to design world

class facilities. At the time I was shocked to realize that the major engineering companies

employed very few if any engineers with practical plant experience. Their design choices

were therefore based on industry accepted practices and often highly antiquated

information.

After working in construction and design I joined a major oil company as a technical

support and production engineer at mid sized oil refinery. During my time at the oil

refinery, we went from operating on conventional light crude to operating on heavy

Canadian oil sands feed stock. I was involved with operations on a daily basis and gained

valuable experience in taking what hardware is available and operating it in such a way to

meet or exceed given KPIs . The fist thing I learned is that just because a label on a

vessel says it is designed for a specific flow does not mean that it will or is currently

operating at that capacity. More often than not units are pushed to 115% of original

design capacity within 6 months of startup to try and push every barrel out of the

refinery.

After assisting with the successful startup and stable operation of the new converted units

at the refinery I decided to join one of the major chemical companies. I was directly

responsible for supporting 3 refineries and assisted with 3 other refineries. This provided Disclaimer of liability: www.crudeoildesalting.com and its authors produced this product as a general guide to crude oil desalting for informational purposes only. All




6

me with invaluable insight to how different oil companies operate and just how

inexperienced many of the operators and engineers were on desalting. During this time I

implemented new chemicals and did numerous trials with different chemicals and

operating strategies. At one facility we literally reduced the oil in brine going to waste

water by 50% over two years to meet the original set target.

At present I am not affiliated with any chemical or desalter hardware vendor and are

therefore able to provide you with a completely unbiased view. The vast majority of the

information provided in this book is general desalting knowledge and industry practice

which I attempted to make available in a single book. Where possible an attempt was

made to add references to other authors to enable further reading.

I hope that this book provides you with the valuable insight and knowledge to operate

your desalter at its maximum efficiency.

Feel free to send me a comment or ask a question at [email protected].

Devlin Jones





7

3. General Desalting Process Overview

The purpose of desalting is to remove contaminants from crude oil before it enters the

processing units. By removing the contaminants at the onset it is possible to minimize

corrosion and fouling in downstream units. Although there can be other objectives the

typical objective in a desalter is to reduce the salt, solids, and metals content while

minimizing oil under carry and water carry over. Oil undercarry is often referred to as oil

in brine or effluent (waste water) and water carry over as the percent water in desalted

crude. In general if a crude feedstock has more than 10 PTB (pounds per thousand

barrels) salt expressed as NaCl is has to be desalted (Gary & Handwerk, 2001). As oil

refineries focus more on long term reliability it is not uncommon for a refinery to desalt

any crude with more than 2PTB salt (Parkash, 2003). The majority of refineries will have

a required corrosion rate and a salt required desalted crude salt content can therefore be

derived.

The vast majority of refineries are configured similarly and will employ either be single

or multistage desalting. The differences can come in the form of hardware and sometimes

how wash water is utilized. There are numerous different manufacturers of desalter, level

instrumentation, mix valves etc. Figures 1 and 2 below shows a typical single and

multistage desalter respectively.





8

Crude oil is typically brought into a refinery by pipeline and goes to the raw crude tanks.

This can be a single tank or multiple tanks with various different crude blended together.

Ideally the crude charge tanks will have continues mixers but some facilities operate with

static tanks which is not advisable since it does not allow for a fully blended feed. The

crude is then pumped into a series of heat exchanges prior to entering the desalter to a

temperature of anywhere from 230-300F depending on the type of crude and the facility.

The crude is then desalted and send through another set of exchanges, then into a crude

charge furnace and finally into the crude unit distillation column.

The desalting process works by mixing raw crude oil with water in a mix valve with a

high differential pressure. This causes the water and oil to form and emulsion with the

salt mostly dissolved in the water phase. This emulsion is then broken in the desalter by

use of gravity, heat, electrical energy and chemical additives.

Understanding how emulsion breaking or phase separation takes place in a desalter is

best described by stokes law. 2)(

92 gR

upp

v fps= where vs is the particle settling

velocity, g is the gravitation constant, pp is the mass density of the settling particles, pf is





9

the density of the bulk fluid, u is the dynamic viscosity and R is the radius of the settling

particles.

From stokes law is then clear that the only parameters that can truly be manipulated is the

difference in density and the particle size. Therefore, the higher the temperature the

bigger difference there will be between the oil and water density and the bigger the water

particles are the quicker they will settle.

CrudeStorage

Crude ChargePumps

1st Stage Desalter

PreheatExchangers

MixingValve

PreheatExchangers Charge

Furnace

AtmosphericDistillation

column

ChemicalInjection

Figure 2. Typical Multi Stage Desalter Setup

2nd Stage Desalter

Brine toDisposal

Fresh Water

Recycledbrine

P-21

Salt Removal

Salt occurs naturally in all crudes but can vary significantly in concentration and makeup

between crudes. A fully sweet synthetic crude that has been hydrotreated can have less

than 2PTB(pounds per thousand barrels) salt while a heavy Canadian Oil Sands crude can





10

easily have 80PTB. The salt comes mainly in the form of CaCl and MgCl though other

forms of salt can be present in smaller quantities.

If the salt is left in the system it will enter the crude charge furnace and will hydrolyze to

form hydrochloric acid. CaCl will typically hydrolyze first with MgCl requiring higher

temperatures. NaCl on the other hand has a high hydrolyzation temperature not normally

reached in a crude charge furnace. For this reason Caustic or NaOH can be injected into

the desalter crude stream to lower overhead chlorides. (Al-Omari, et el.., 2008):

The basic stoichiometric equations are as follows

CaCl2 + 2H2O -> 2HCl + Ca(OH)2

CaCl2 + H2O -> 2HCl + CaO *Ca can be substituted for Mg and Na to give the same reactions.

It is clear from these equations that the amount of salt going into the charge furnace must

be controlled to minimize corrosion in the downstream equipment. Since facilities are

designed for a specific corrosion allowance it is critical that salt and corrosion is

controlled to stay at or below the design limits.

A single stage desalter can typically remove up to 95% of salt while a two stage desalter

can typically remove up 99% (Gary & Handwerk, 2001). If you require more than 99%

you may need to add another desalter but this is generally not done since you will see a

very small incremental increase in salt removal. It is important to understand that the

third desalter is usually not cost effective since the incremental salt removal is so small

and the use of corrosion inhibitors or metal upgrades may be more effective.

Sediment and BS&W Removal





11

Unless you are using a 100% hydrotreated synthetic crude oil you will probably have

sediment issues to deal with. Even the clean hydrotreated crude can have some sediment

picked up from dirty pipelines and tanks. The reason hydrotreated oil is free from

sediment is because it went through a hyrotreating reactor with catalyst in it which serves

as a filter for sediment and some metals.

The problem with high amounts of sediment is quite obvious. All the sediment going

though the desalter will get deposited somewhere downstream in the system causing

fouling. It is common to have sediment buildup in downstream heat exchangers and

furnaces. In some cases you may even carry the sediment through to the crude column.

Though it would be nice to remove 95-98% of solids it is however rarely achieved and a

normal expectation is to see about 60% solids removal although some sites regularly

removes up to 80% solids (Gary & Handwerk, 2001). The main reason for a limit on

solids removal is that you have to keep increasing your mixing energy to achieve higher

solids removal. At some point with continuous increases of mixing energy you will start

to see a reduction in solids removal and desalting efficiency forcing you to cut back.

Figure 3 gives a graphical representation of this phenomenon. Keep in mind that it is a

general graph that should be plotted for a specific facility. Creating such a graph for your

facility is likely not possible but portions of the graph can be generated with historical

data. Then by understanding the mixing dynamics adjustments can be made your mixing

energy for optimal operation.





12

Mixing Energy Relationship with Desalted Crude Salt and BS&W Content

0

20

40

60

80

100

120

Mixing Energy

% S

alt i

n D

esal

ted

Cru

de

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

%B

S&W

% Salt % BS&W

Optimal Operating Point

Figure 3. Mixing Energy Relationship with Desalted Crude Salt and BS&W content.

(Paul et. el, 2004)

In general the first of objective of a desalter is to maximize desalting efficiency. Once

this is achieved, focus is applied to removing more solids and other contaminants. There

may be some middle ground but it is almost never a good idea to send excess salt into a

distillation column to achieve higher sediment removal.

Metals and other Contaminant Removal

There is usually some correlation between an increase in solids removal and a higher

degree of metals and other contaminants removal. The problem with metals is typically

related to downstream unit limitations. Some metals will for example act as catalyst

poisons and lead to premature catalyst degradation costing the facility millions in catalyst

change outs and production losses. Disclaimer of liability: www.crudeoildesalting.com and its authors produced this product as a general guide to crude oil desalting for informational purposes only. All




13

This is a Free Ebook

This free Ebook is available for from www.crudeoildesalting.com/blog and contains the first 3 chapters of the full Crude Oil Desalting ebook.

To obtain a copy of the full ebook and all the chapters listed in the table of contents

please visit www.crudeoildesalting.com

Devlin Jones, [email protected]

free-ebook-crude-oil-desalting.pdf

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